U.S. patent number 4,276,369 [Application Number 05/957,836] was granted by the patent office on 1981-06-30 for photo--imaging a polymethyl isopropenyl ketone (pmipk) composition.
This patent grant is currently assigned to Tokyo Ohka Kogyo Kabushiki Kaisha. Invention is credited to Yoichi Nakamura, Minoru Tsuda.
United States Patent |
4,276,369 |
Tsuda , et al. |
June 30, 1981 |
Photo--imaging a polymethyl isopropenyl ketone (PMIPK)
composition
Abstract
The present invention relates to a method for forming ultra fine
patterns on films of polymethyl isopropenyl ketone or a mixture of
polymethyl isopropenyl ketone and a benzophenone compound by
exposing such films to ultra violet rays in the range of from 1,000
to 3,500 A. The present invention is particularly useful for
providing semiconductors having ultra fine patterns and ultra
LSI's. The electric or electronic circuits for electronic or
electric apparatus and equipment have been produced by wiring
resistors, condensers, coils, vacuum tubes and the like necessary
components. However, because of various disadvantages such as
assembly requiring much time, complication of work, necessity of
using large equipment, reasons or causes for errors, limitation of
productivity, impossibility of reducing price or cost and the like,
the present invention has been developed for printed circuit
boards. However, in the present invention, such active devices as
vacuum tubes, resistors, condensors, coils and the like must be
fixed on printed circuit boards which have been previously
finished. Therefore, although this invention has brought reduction,
to some extent, in the time required for the work, complication of
work, and the work capacity (scale), it can not yet be said that it
has made the work miniaturized or economical. Under such
circumstances, through the invention of diodes and transistors by
solidification of rectification and amplifying functions in the
form of germanium or silicone semiconductors, it has become
possible to make the work extremely miniaturized.
Inventors: |
Tsuda; Minoru (Isehara,
JP), Nakamura; Yoichi (Samukawa, JP) |
Assignee: |
Tokyo Ohka Kogyo Kabushiki
Kaisha (Kawasaki, JP)
|
Family
ID: |
15076495 |
Appl.
No.: |
05/957,836 |
Filed: |
November 6, 1978 |
Foreign Application Priority Data
|
|
|
|
|
Nov 4, 1977 [JP] |
|
|
52-132234 |
|
Current U.S.
Class: |
430/326;
430/270.1; 430/926; 522/45; 522/150; 430/313; 430/925; 430/940;
522/46 |
Current CPC
Class: |
G03F
7/039 (20130101); Y10S 430/124 (20130101); Y10S
430/143 (20130101); Y10S 430/127 (20130101); Y10S
430/126 (20130101); Y10S 430/141 (20130101) |
Current International
Class: |
G03F
7/039 (20060101); G03C 005/00 () |
Field of
Search: |
;430/270,296,313,326,323,940,942,925,926 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Schultz, Journal of Polymer Science, vol. XLVII, pp. 267-276,
(1960). .
Lin, Deep VV Lithography, J. Vac. Sc. Technol., vol. 12, No. 6,
Nov./Dec. 1975. .
Levine et al., "The Interaction of 5 Kev. Electrons with Polymers
of Methyl Isoproponyl Ketone", Oct. 24-26, 1973. .
Harper et al., "Mechanism of the Benzophenone-Sensitized
Photodegradation of Polypropylene", J. of App. Polymer Sci., vol.
17, p. 3503,1973. .
Wissbaun, Journ. of American Chemical Soc., 81, 58 (1959). .
Lin, "Deep-VV Conformable-Contact Photolithography for Bubble
Circuits", Conformable Masks, May, 1976. .
Heskins et al., "Photodegradation of Styrene-Vinyl Ketone
Copolymers", ACS Symposium Series No. 25, pp. 281-289,
(1976)..
|
Primary Examiner: Kimlin; Edward C.
Attorney, Agent or Firm: Armstrong, Nikaido, Marmelstein
& Kubovcik
Claims
What is claimed is:
1. A process for forming an ultrafine pattern which comprises
exposing a film of a mixture of polymethyl isopropenyl ketone
having a molecular weight of from 10,000 to 1,000,000 and
dispersity index of below 3 and a benzophenone compound of the
general formula: ##STR2## wherein X.sub.1, X.sub.2, X.sub.3 and
X.sub.4 independently represent hydrogen atom, a halogen atom, a
lower alkyl group, a lower alkoxy group or hydroxyl group, to
irradiation with ultraviolet rays having a wave length in the range
of from 1,000 to 3,500 A through a mask pattern and subjecting the
resulting film to a solvent removal process whereby said film is
subjected to a suitable solvent which dissolves said film which has
been exposed to said ultraviolet rays.
2. A process according to claim 1 wherein the benzophenone compound
is selected from the group consisting of benzophenone,
4-chlorobenzophenone, 4-bromobenzophenone,
2,4-dichlorobenzophenone, 2,4'-dichlorobenzophenone,
4,4'-dibromobenzophenone, 4-hydroxybenzophenone,
4,4'-dihydroxybenzophenone, 4-methylbenzophenone and
4,4'-dimethylbenzophenone.
3. A process according to claim 1 wherein the irradiation is
effected under vacuum or in an inert gas atmosphere.
Description
BACKGROUND OF THE INVENTION
Through further development of diodes and transistors in the form
of semiconductor electronic and electric circuits have been
solidified to be so-called Integrated Circuits (ICs). ICs are
mainly made from silicon because of easy handling, rich resource
and other good reasons. ICs have met the applicants highest
expectations for solidification of circuits, reduction of manpower,
miniaturization, less trouble, economy by mass production and the
like, and they are currently widely used in electronic and electric
circuits, memories for computers, microcomputers and other
components. In the manufacturing processes of such semiconductor
devices as above, there is a technology called "photolithography".
In photolithography, after having coated about 1 .mu.m thin film of
a photoresist, which will become an etching resist, on a silicon
wafer which has a silicon oxide film of several 1,000 A, the film
is exposed to ultraviolet rays through a mask and images are
developed and etched. After having stripped off the photoresist,
the wafer is completely cleaned, and dopants are diffused and
implanted into from the exposed area of silicon. By repeating this
photolithography several times and, furthermore, by preparing
electrodes and wiring, ICs are manufactured. The working geometry
or size of photolithography of diodes, transistors and early ICs
produced rough figures as 100--scores of .mu.m. Since then, after
the superiority of solidified devices had been recognized, a
further miniaturization has been made by adding the same functions
and/or new functions, efforts were made for increasing the
economical aspects, and development has been made for new demands.
For this reason, together with the improvement and increase of mask
performance, photoresist performance, quality of silicon wafers,
performance of mask alignment equipments, diffusion techniques,
performance of related chemicals, etching techniques and the like,
it has become possible to work for the geometries of 10-4 .mu.m
with necessary working accuracy and resulted in the form of Large
Scale Integrated Circuit (LSI).
As LSI continuously shows expected performance and economy as a
solid device the development of Ultra LSI (commonly expressed as
Very Large Scale Integrated Circuits) has recently become very
active by making the working geometry of the lithography such that
much finer patterns of more limited results of 3-1 .mu.m or below 1
.mu.m with necessary working accuracy can be produced.
In conventional photolithography, because ultra violet rays having
wavelengths of from 3,500 to 4,500 A are used they produce
diffraction of light and other undesired phenomena, and it has been
concluded that it would be impossible to form fine patterns of
below 1 .mu.m even if modification or improvements are made or with
full utilization of high performance of conventional
photolithography. Particularly in the case of mass production, the
present invention can provide economical advantages and increase
demand and it meets the subject purpose or object, but the
extension of conventional techniques cannot provide mass production
fine patterns of 1 .mu.m.
In order to obtain resolution of below 1 .mu.m by avoidance of
light diffraction to solve the above problem, development is under
progress for the application of various energy sources such as
electron beam which has a much shorter wavelength than light
(approximately 0.5 A) and soft X rays (about 10 A). To explain this
development in detail, application of electron beams requires large
scale equipment which must be operated and used by large scale
computers resulting in an extremely expensive system, and in
addition to these disadvantages, although there are many available
electron beam resists there is no acceptable one, it requires
longer exposure times, and there is no practicality in the transfer
of images onto the wafers. Furthermore, there is no practical light
source (energy source) for application of soft X rays. It has a
number of disadvantages such as mask-making is troublesome,
mask-adjusting is difficult, there is a physiological dislike,
extremely expensive equipment is anticipated and others. For these
reasons, a working technique for an economical mass production of 1
.mu.m or below 1 .mu.m geometry using energy of shorter wavelengths
is still considerably difficult to be developed.
In order to solve such existing problems, through utilization of
ultra violet rays having a shorter wavelength of from 1,000 to
3,500 A than from 3,500 to 4,500 A as used in the conventional
photolithography, and a special photoresist such as Polymethyl
Methacrylate (PMMA), it has been discovered that, by reduction of
diffraction phenomenon, it is possible to obtain ultra high
resolution and a highly accurate resist pattern of 1 .mu.m down to
below 1 .mu.m.
However, although ultra fine patterns could be obtained with a
single position exposure instead of using a scanning exposure, PMMA
was in a disadvantageous position because of its considerably low
sensitivity, lack of etching resistance, especially lack of
resistance against plasma dry etching, therefore, it could not be
used in practical applications.
Because of these reasons, if a photoresist having equivalent to or
higher ultra resolution, sensitivity and etching resistance than
PMMA against the light source with wavelengths of 1,000-3,500 A,
could be found, such a photoresist can be used in the technology of
extended conventional photolithography and, in addition to such
advantage, because low pressure mercury lamps, deutrium lamps,
xenon-mercury lamps and the like, can be used as light sources and
it becomes possible to solve the problems with the most economical
formation of ultra finer patterns and its practicality.
With such background as mentioned above, the inventors of the
present invention, as the result of their research and development,
have invented a method to form extremely superior ultra fine
patterns without having any one of the above-mentioned defects.
SUMMARY OF THE INVENTION
To explain it in brief, the inventors have found a completely new
photoresist which can form ultra fine patterns by application of
ultra violet rays having wavelength in the range of from 1,000 to
3,500 A. The new photoresist is prepared from polymethyl
isopropenyl ketone (PMIPK) which, has been found to have about 20
times higher sensitivity than PMMA when exposed to ultra violet
rays having wavelengths of from 1,000 to 3,500 A as well as ultra
high resolution (it is dependable upon the quality of masks, but it
can give ultra high resolution below 1 .mu.m down to 0.4 .mu.m-0.2
.mu.m) equivalent to PMMA, and furthermore, another important
property of dry-etching resistance is about 2-3 times higher than
that of PMMA, making it a superior material.
Research has been made on the basic data of light degradation of
PMIPK but nothing has been mentioned or nothing has been found at
all on the method to form ultra fine patterns and properties to be
used as etching resist, nothing has been mentioned or nothing has
been found on the necessary information for the present invention
such as a method to form ultra fine patterns and properties to be
used as etching resist.
Although it has already been found that PMIPK is decomposed upon
exposure to electron beams under a vacuum there was no knowledge
about the possibility nor was any trial attempted to decompose
PMIPK with ultra violet rays to form ultra fine patterns.
Furthermore, the inventors have also found that a mixture prepared
by the addition of benzophenone derivatives to PMIPK will increase
considerably the degree of sensitivity, reduce the degree of
swelling during development, form more stable images and give much
superior etching resistance; the inventors have completed the
present invention based upon these discoveries.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for forming an ultrafine
pattern wherein a film of polymethyl isopropenyl ketone having a
molecular weight of 10,000-1,000,000 (and dispersity index of below
3 which is an indication of the distribution of the molecular
weight) is irradiated with ultraviolet rays having a wave length in
the range of from 1,000 to 3,500 A through a mask pattern and then
it is subjected to a developing treatment.
The polymethyl isopropenyl ketone used as the principal component
of the sensitive material according to the present invention is a
polymer having a molecular weight of 10,000-1,000,000 and
dispersity index of below 3 obtained by polymerizing methyl
isopropenyl ketone. If this polymer is irradiated with ultraviolet
rays having a wave length in the range of from 1,000 to 3,500 A, it
is decomposed and as a result, it becomes easily soluble in a
solvent such as a mixture of cellosolve and cyclohexanone. The film
thus prepared has a thickness of usually 0.3-1.0.mu..
If the molecular weight of PMIPK of the present invention is lower
than 10,000, it shows a poor film-forming property, while if it is
more than 1,000,000 it shows a poor solubility in solvents; thus,
it is quite inconvenient for handling and it is difficult to make
thick films. For these reasons, it is more convenient and desirable
to use PMIPK which has a molecular weight in the range of from
30,000 to 600,000. In order to obtain superior resolution, it is
more advantageous to use PMIPK having a small distribution of
molecular weight; in other words, the dispersity index (Mw/Mn in
which Mw=weight-average molecular weight, and Mn=number-average
molecular weight) which shows the distribution of molecular weight,
is required to be below 3. It is desirable if it is below 2. When
it is more than 3 or 4 the resolution will be definitely reduced.
PMIPK with these properites, in case it is in complete contact with
a mask, should have an ideal property whereby it shows no staining
of the mask with tackiness of a regular photoresist or cracking
caused by scratches or brittleness of the photoresist. This
property is extremely advantageous in the forming of ultra fine
patterns through increased yield in the work process and
possibility of complete contact with a mask.
A light source used for the image-forming exposure according to the
process of the present invention may be any light source which
provides ultraviolet rays having a wave length in the range of from
1,000 to 3,500 A, for example, a low pressure mercury lamp having a
window of MgF.sub.2, SiO.sub.2 or LiF, a heavy hydrogen lamp or a
xenon-mercury lamp. A mask pattern used in the image-forming
exposure may be prepared by providing a desired pattern on a base
made of LiF, MgF.sub.2, CaF.sub.2, BaF.sub.2, Al.sub.2 O.sub.3 or
SiO.sub.2 which transmits light having a wave length in the range
of from 1,000 to 3,500 A.
The image-forming exposure treatment is effected advantageously
under vacuum or in an inert gas atmosphere. As the inert gas, there
may be used, for example, nitrogen, helium, argon and xenon.
The image-forming exposure treatment is usually completed by
irradiation for a period of time ranging from one second to five
minutes, though the irradiation time depends on size and kind of
light source, kind of the mask, molecular weight and dispersity
index of below 3 of the polymethyl isopropenyl ketone and thickness
of the film.
After the image-forming exposure treatment has been completed, the
film is subjected to a developing treatment. The developing
treatment is effected by washing with a solvent in which the
decomposition product formed by the irradiation with ultraviolet
rays of 1,000-3,500 A is soluble, but in which the polymethyl
isopropenyl ketone is insoluble, for example, a mixture of
cellosolve or cyclohexanone. For the washing process, any means
such as immersion, spraying or brushing can be employed.
More preferred results can be obtained by incorporating as a
sensitizer a benzophenone compound of the general formula: ##STR1##
wherein X.sub.1, X.sub.2, X.sub.3 and X.sub.4 each represent a
hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy
group or hydroxyl group in m- or p-position in the polymethyl
isopropenyl ketone used as the sensitive material. As the
benzophenone compounds, there may be employed, for example,
benzophenone, 4-chlorobenzophenone, 4-bromobenzophenone,
2,4-dichlorobenzophenone, 2,4'-dichlorobenzophenone,
4,4'-dibromobenzophenone, 4-methylbenzophenone,
4,4'-dimethylbenzophenone and 4-hydroxybenzophenone. Among them,
4,4'-dibromobenzophenone is particularly preferred. The
benzophenone compounds may be used either alone or in the form of a
combination of two or more of them. The amount of the benzophenone
compound(s) is usually selected in the range of from 1-25 parts by
weight per 100 parts by weight of the polymethyl isopropenyl
ketone. The incorporation of the benzophenone compound brings about
the advantages that a strong developing solution can be used and
etching resistance of the film is improved, since wetting in the
developing step is reduced. In drying the film, if a high
temperature heat drying process is employed, the sensitizing effect
of the benzophenone compound cannot be exhibited sufficiently
sometimes. In such a case, the film is treated with a vapor of a
solvent compatible with the polymethyl isopropenyl ketone such as
the vapor of cyclohexanone. As a matter of course, such a problem
is not caused in a low temperature drying process. Further, some
benzophenone compounds, for example, 4,4'-dibromobenzophenone,
exhibit a complete sensitizing effect even if it is dried at a high
temperature.
According to a preferred embodiment of the present invention, a
solution of polymethyl isopropenyl ketone or a mixture of
polymethyl isopropenyl ketone and a benzophenone compound of the
above general formula in a suitable solvent such as cyclohexanone
is applied to a base such as a silicon wafer, dried to form a
resist layer of a thickness of 0.3-1.mu., subjected to an
image-forming exposure treatment with a sterilization lamp which
emits an ultraviolet ray having a wave length of 2537 A and then
subjected to a baking treatment to remove the solvent from the
resist layer. Therefore, it is immersed in a developer such as a
mixture of cellosolve or cyclohexanone to elute the exposed part,
thereby obtaining a very minute pattern.
Thus, according to the present invention, submicron patterns can be
formed in a short period of time by using a light source easily
available on the market at a low price such as a heavy hydrogen
lamp or low pressure mercury lamp (sterilization lamp). Further,
the patterns thus obtained are sufficiently resistant to etching
caused by hydrofluoric acid or the like.
Moreover, since it can resist plasma dry etching which is an
inevitable process in the etching of ultra fine patterns, it can be
suitably utilized in the fabrication (manufacture) of ultra
LSI.
The following examples further illustrate the present
invention.
EXAMPLE 1
100 Parts by weight of polymethyl isopropenyl ketone of a molecular
weight of 800,000 and dispersity index of 1.7 were dissolved in
cyclohexanone to obtain a solution of a concentration of 10 weight
%. 10 Parts by weight of a benzophenone compound shown in Table 1
were added to the solution and the mixture was subjected to
filtration through a filter of 0.2.mu. to obtain a sensitizing
solution. The sensitizing solution was then applied to a silicon
wafer with a spinner. A resist layer of a thickness of about
0.5.mu. was formed thereon and the whole was dried in a desiccator
under reduced pressure for about two hours. The resulting sensitive
material was exposed stepwise from a distance of 5 cm to a
commercial sterilization lamp emitting an ultraviolet ray having a
wave length of 2537 A. After exposure, it was subjected to a baking
treatment at 80.degree. C. for 40 minutes to remove the solvent
completely from the resist layer.
Then, the silicon wafer was immersed in a developing solution
comprising ethyl cellosolve and cyclohexanone in a proportion of
7:3 for one minute to effect the development and subsequently
washed with water for one minute. Sensitivity was determined from
the number of residual steps. The results are shown in Table 1.
Relative sensitivity in the table is a relative value based on
sensitivity (10) of pre-baked polymethyl isopropenyl ketone.
TABLE 1 ______________________________________ Relative No.
Benzophenone compound sensitivity
______________________________________ 1 None 10 2 Benzophenone 18
3 4-Chlorobenzophenone 18 4 4-Bromobenzophenone 14 5
2,4-Dichlorobenzophenone 18 6 2,4'-Dichlorobenzophenone 14 7
4,4'-Dichlorobenzophenone 18 8 4,4'-Dibromobenzophenone 35 9
4-Methylbenzophenone 18 10 4,4'-Dimethylbenzophenone 18 11
4-Hydroxybenzophenone 12 12 4,4'-Dihydroxybenzophenone 12
______________________________________
It has been found that 4,4'-dibromobenzophenone of No. 8 in the
above list, is especially effective.
EXAMPLE 2
A resist layer comprising 100 parts by weight of polymethyl
isopropenyl ketone and 10 parts by weight of
4,4'-dibromobenzophenone was prepared under the same conditions as
in Example 1. Baking treatment was effected at various temperatures
for various periods of time. The results are shown in Table 2.
TABLE 2 ______________________________________ Baking conditon
Relative No. Temperature (.degree.C.) Time (minute) sensitivity
______________________________________ 1 80 20 35 2 80 40 35 3 85
40 35 4 90 40 35 5 100 40 35
______________________________________
It is apparent from the above table that the resist layer is not
changed in sensitivity by the baking treatment.
EXAMPLE 3
A resist layer comprising the same polymethyl isopropenyl ketone
and benzophenone compound as in Example 1 was prepared. It was
subjected to a baking treatment at 80.degree. C. for 40 minutes and
then to exposure treatment with the same sterilization lamp as in
Example 1. Sensitivity of the product was determined. The results
are shown in Table 3. Separately, the baked resist layer was
contacted with cyclohexanone vapor at 80.degree. C. for 10 seconds
and then subjected to the exposure treatment. Sensitivity thereof
was determined to obtain the same results as in Table 1. In other
words, even if the sensitivity was lowered once by the baking
treatment, except for the case of using 4,4'-dibromobenzophenone,
the sensitivity could be recovered by treating the film with an
excellent solvent such as cyclohexanone.
TABLE 3 ______________________________________ Relative sensitivity
After treat- After ment with No. Sensitizer baking solvent vapor
______________________________________ 1 None 10 10 2 Benzophenone
12 18 3 4-Chlorobenzophenone 10 18 4 4-Bromobenzophenone 10 14 5
2,4-Dichlorobenzophenone 10 18 6 2,4'-Dichlorobenzophenone 10 14 7
4,4'-Dichlorobenzophenone 12 18 8 4,4'-Dibromobenzophenone 35 35 9
4-Methylbenzophenone 12 18 10 4,4'-Dimethylbenzophenone 10 18 11
4-Hydroxybenzophenone 9 12 12 4,4'-Dihydroxybenzophenone 9 12
______________________________________
It is apparent from the above table that sensitivity is reduced
after the baking treatment, except for the case of using
4,4'-dibromobenzophenone but the sensitivity could be recovered by
the solvent vapor treatment.
EXAMPLE 4
10 Parts by weight of 4,4'-dibromobenzophenone, per 100 parts by
weight of polymethyl isopropenyl ketone, were added to a 10 weight
% solution of polymethyl isopropenyl ketone of a molecular weight
of 500,000 and dispersity index of 1.8 in cyclohexanone to obtain a
sensitizing solution. The sensitizing solution was applied to a
silicon wafer in the same manner as in Example 1 and then baked at
80.degree. C. for 20 minutes to obtain a resist layer of a
thickness of about 0.5.mu.. Thereafter, a quartz mask pattern was
applied closely to the resist layer. After exposure to a light
emitted by the same sterilization lamp as in Example 1 for one
minute, it was immersed in the same developing solution as in
Example 1 for one minute to effect the development. After washing
with water for one minute followed by drying, a very accurate
pattern of a width of 0.5.mu. was obtained.
The silicon wafer having the formed pattern was baked at
170.degree. C. for one hour and then treated with an etching
solution containing hydrogen fluoride and ammonium fluoride (weight
ratio 1:6) for 7 minutes.
Thus, an etching pattern matching the mask pattern was
obtained.
EXAMPLE 5
A photoresist prepared by dissolving PMIPK having a molecular
weight of 200,000 and dispersity index of 2.3 in cyclohexanone was
pre-baked for 20 minutes at 110.degree. C. and spin-coated in such
a way that a film thickness of 0.5 .mu.m was obtained in the same
way as for practical example No. 1.
A comparison was made to see if this film can resist plasma dry
etching which is an inevitable and important property required in
the etching of ultra fine patterns, compared with the 0.5 .mu.m
film of the aforementioned PMMA (molecular weight: 1,000,000) also
coated on a silicone wafer. The etching machine used in this
comparison, was a wafer-fed precision plasma etching machine (Tokyo
Ohka's Ohka Automatic Plasma Machine [OAPM]) which is one of the
best equipment available at present.
In the working geometry for highly accurate memories, patterns of
2-4 .mu.m are etched, but in case of poly silicone a thickness of
3,000-5,000 A and in case of silicone nitride a thickness of
1,000-1,200 A are generally used. The etching of these thicknesses,
with use of OAPM, can be completed with such an accuracy that a
slight under-cut can be ignored, in about 40 seconds in case of
poly silicon of 3,500 A and about 60 seconds in case of silicone
nitride of 1,200 A respectively under conditions of RF (high
frequency) output: 200 W, etching gas: CF.sub.4 (95%)+O.sub.2 (5%)
with 1 l/min. flow, wafer temperature: 130.degree. C., vacuum: 0.5
Torr.
The aforementioned PMIPK and PMMA were spin-coated onto wafers and
tested for etching resistance for comparison purposes. The results
are shown in the following table.
______________________________________ Reduction of film thickness
1 min. 2 min. 3 min. ______________________________________ (1)
PMMA 0.125 .mu.m 0.206 .mu.m 0.290 .mu.m (2) PMIPK 0.008 .mu.m
0.064 .mu.m 0.112 .mu.m (1)/(2) 15.6 3.2 2.6
______________________________________
Judging from the result of this test, it has been found that PMIPK
when it is plasma-etched with OAPM showed almost equal reduction of
film thickness (0.12 .mu.m/3 min) as well as the photoresists
(cyclized rubber type) used for fabrication of semiconductors and
is very close of 0.08 .mu.m/3 min. of the best positive type
photoresist, and it can be successfully used in the practical
application while PMMA can not be used in practical application
because it showed extremely more reduction in film thickness with
uncertainty of its performance.
EXAMPLE 6
The same PMIPK photoresist was spin-coated to form a 0.5 .mu.m
thickness as used in example No. 1, on a wafer having silicon
nitride (SiN) of 1,000 A on the surface of SiO.sub.2 over a silicon
wafer. After treatment as in example No. 1, and processing as in
example No. 4, a window pattern of 0.4 .mu.m was obtained with good
accuracy. The same photoresist was etched on aforementioned SiN
with a water-fed precision plasma etching equipment (such as Tokyo
Ohka's OAPM-300) under the following conditions:
RF output: 200 W
Gas: CF.sub.4 1.0 l+O.sub.2 50 ml (5%)
Vacuum: 0.55 Torr.
Temperature: 120.degree. C.
Etching of SiN of 1,000 A was completed in an actual etching time
of 30 seconds. The results show that the PMIPK photoresist can
resist etching and provides ideal etching without any
side-etching.
* * * * *